Publicist: She'll also receive radiation, but doctors optimistic

"I am inspired by the brave women who have faced this battle before me and grateful for the support of family and friends," she said in a written statement. "I am joining the more than 200,000 women who will be diagnosed with breast cancer this year."

Crow, who turned 44 this month, will receive radiation treatments as a precaution, but her doctors are optimistic, Dave Tomberlin of Interscope Geffen A&M Records said in a statement.

The singer is postponing her North American tour scheduled for March and April, but Tomberlin said, "It is Sheryl Crow's intention to reschedule as much of the tour as reasonably possible."

Crow and Armstrong announced their engagement in September, but issued a statement earlier this month saying, "We have made a very tough decision to split up." It would have been her first marriage and his second.

Armstrong, 35, also has battled cancer. He overcame testicular cancer that had spread to his lungs and brain and went on to become the most dominant athlete in cycling in recent years.

His seven straight Tour de France titles from 1999 to 2005 are a race record. He retired after winning his last race, with Crow cheering him on.